U.S. Pat. No. 4,465,749 issued Aug. 14, 1984 to J. W. May and Y. S. Ng, discloses a method of amplifying an electrostatic image using charge injection toners. This patent application is an improvement of that method, and that patent is incorporated by reference herein.
According to U.S. Pat. No. 4,465,749, a weak electrostatic image is formed by exposing a charged photoconductive member, for example, an image formed from exposure to starlight, a radiographic image using very low exposure, or an exposure of an intensity comparable to those in conventional photographic cameras. This weak exposure creates an image having a voltage differential as small as 20 volts between the image areas and the background areas. That image is toned with a charge injection toner creating a weak toner image which would ordinarily not be particularly useful because it is barely visible. The weak toner image is fused to the photoconductor and the photoconductive member is recharged. The charge injection characteristics of the toner cause charge to leak through the toner and the photoconductive member to ground creating a substantially enhanced electrostatic image which can be toned. Amplifications are possible with this approach of 5-30 times with good resolution. Using this method overall system speeds were obtained comparable to that available with ordinary ASA 100 silver halide photographic film.
The amplified toner image can be transferred to a receiving sheet. Additional copies of the same image can be made from the same low density fused image using a form of xeroprinting. However, the imaging member itself is not readily reusable for a new image because of the fused image of charge injection toner. Although processes are known in which masters for xeroprinting are reused by using solvents or scraping action to remove the toned image, such steps greatly restrict the materials usable and are not considered practical.